1. Field of the Invention
The present invention relates generally to surgery and more specifically to image analysis through computer assisted medical diagnostics.
2. Related Art
Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging technology that uses electromagnetic fields to create one or more high contrast cross-sectional images or slices of the internal anatomy. Using automated, semi-automated or manual processing techniques, the images can be stacked, segmented and otherwise processed to create computer assisted design (CAD) models or other types of three-dimensional models of the anatomy of interest. For instance, MRI images can be processed to create a three dimensional model of the surface contours and geometries of the bone and/or cartilage of a patient's joint. Other types of non-invasive imaging techniques can be used to create three dimensional models of bones, joints and other anatomy as well, including, without limitation, Computed Tomography (CT) imaging or ultrasound imaging.
It is known to use three-dimensional models in some instances to create orthopaedic implants and/or instrumentation that is adapted to specifically correspond to the anatomy of a particular patient. For instance, it is known to use three-dimensional models of a femur and/or tibia to build one or more cutting guides with an anatomy-contacting surface that is specifically designed to reference and correspond to the anatomy of a particular patient and to guide a cutter to form one or more resections on the bone in desired positions and orientations relative to that anatomy and certain important axes of that anatomy. Three-dimensional models and other information obtained from these non-invasive imaging techniques can be used in other contexts as well outside of the development of patient specific instruments and implants.
In some instances, it may be important for the patient to remain as motionless as possible during imaging, as movement can create inaccuracies in the process that could potentially negatively impact on the later use of the information obtained from the imaging to treat the patient. For instance, when an MRI procedure is used to obtain information to create a patient specific instrument for facilitating a knee arthroplasty procedure, it is, at least in some procedures, necessary to scan several portions of the patient's anatomy, such as, in some cases, the ankle, knee and hip. In some instances, it may be important to maintain the spatial relationship between the ankle, knee and hip scans to determine an appropriate position and orientation of the patient specific instrument or other orthopaedic device. For instance, in some instances, those relationships may be used to determine a mechanical axis, anatomic axis, or other important axis of the knee joint, or other references associated with this or other portions of the anatomy, which may be, in some cases, important references and information for properly aligning a cutting guide or other instrument or implant with respect to the bone. For instance, knowing the mechanical axis of the knee joint may be important for establishing the varus/valgus alignment of the cutting guide or other degrees of freedom associated with the positioning and orienting of the cutting guide in three dimensional space. If the patient moves during one of the scans, or in between one of the scans, it may change the relationship between the anatomy associated with the ankle, knee and/or hip with respect to the data obtained through the imaging procedure, and could potentially negatively impact on the quality of the data obtained, and consequently the quality of the patient specific instrument or implant created using that data.
In some procedures, an additional x-ray of the entire leg or other anatomy of interest may be performed as a check against the possibility that the relationship between the relevant anatomy changed during the imaging procedure. The additional x-ray adds expense to the pre-surgical planning, and there remains a need in the art for a way to verify the relationship between the relevant anatomy did not change during the imaging procedure at a lower cost.